There is no way to control wich users can set the notification email address for messages outputs.
The email message output can be turned off, but then no emails will be sent to any users. Also, the messaging profile edition can be turned off, but then no users will can change any notifications preferences. We (Universidade Federal de Santa Catarina, Brazil) need a capability to disallow users to edit their email message but still allow to configure other messaging profile options. We need this change because our users must not edit their email via Moodle (and this is locked on their profile). Also, the change of this email is not confirmed, so users can set any email there.